It is known to use bipolar RF energy devices that clamp tissue between opposed electrodes and apply RF energy to heat tissue to form lines of ablation on the tissue. This has found particular application in the formation of strategically located lines of ablation in cardiac tissue to block spurious electrical signals to the heart, which has been particularly beneficial in the treatment of atrial fibrillation. See, e.g., U.S. Pat. No. 6,889,694 which is incorporated herein by reference.
Such bipolar electrode devices apply energy directly to the surface of tissue clamped between a first electrode and a second electrode. The first electrode, the clamped tissue, and the second electrode form a conductive resistive circuit. As the moisture in the tissue conducts the RF energy, the tissue begins to desiccate. As the tissue desiccates it becomes more resistive. The application of bipolar RF energy on tissue shows that tissue desiccation progresses inwardly from the outside or surface of the tissue near the electrode-tissue contact area, where the current flux or density is greatest. Surface desiccation increases resistance in the tissue and can make it more difficult to achieve good depth of penetration in underlying tissue without creating a larger than desired area of ablated tissue or excessive surface heating adjacent to the electrodes. A recent study reported that to achieve a depth of ablation of 5 mm, a width of ablation of almost 8 mm wide in the endocardium resulted. See, “Mechanism, Localization, and Cure of Atrial Arrhythmias Occurring After a New Intraoperative Endocardial Radiofrequency Ablation Procedure for Atrial Fibrillation,” Thomas, et al., Journal of the American College of Cardiology, Vol. 35, No. 2, 2000, hereby incorporated by reference. While a wider ablation facilitates the surgeon's visual confirmation that an ablation has been created, it is still desirable to control the width of ablation so as to keep the width of the ablation and thermal spread from the zone of ablation within certain limits so as to not irreversibly damage more cardiac tissue than necessary.
To overcome surface tissue heating effects, techniques such as cooling or cryogenics have been used, and selected positioning of the electrodes has been considered. See, for example, U.S. Pat. No. 6,413,253 to Koop et al., U.S. Pat. No. 6,629,535 to Ingle et al., and U.S. Pat. No. 7,022,121 to Stern et al. and U.S. Pat. No. 6,918,906 to Long.
Consequently, a significant need exists for an improved electrosurgical device and method of use that can enhance lesion formation and provide for more efficient ablation.